Ferromagnetic elements are used, for example, to form non-volatile memory cells. A magnetic element typically includes bottom and top magnetic layers separated by a non-magnetic layer. The non-magnetic layer, for example, comprises an insulating material to form a magnetic tunnel junction (MTJ) type element. First and second conductors are magnetically coupled to the top and bottom magnetic layers to from a magnetic memory cell. One conductor is referred to as the bitline and the other is referred to as the wordline. The bitline and wordline are orthogonal to each other. A plurality of magnetic elements are interconnected by wordlines and bitlines to form an array.
The magnetic layers of an element are formed with magnetic vectors along an easy axis. The magnetic vector of one layer is fixed in a first direction along the easy axis (e.g., reference or fixed layer) and the magnetic vector of the other layer can be switched between first and second opposite directions along the easy axis (e.g., storage layer). As such, the magnetic vectors in the layers can be oriented parallel or antiparallel to each other. The top magnetic layer with switchable magnetic vector is referred to as the storage or free layer.
The direction of the vector in the storage layer can be switched by the application of a magnetic field generated by passing a current through one or both conductors. Depending on the magnetic field generated, the magnetic vector in the second layer either switches direction or remains the same. The magnetic element would have a first or second resistance value based on whether the magnetic vectors are oriented parallel or anti-parallel, representing a first or a second logic state being stored. For example, the magnetic element will have a high resistance value when the vectors of the layer are antiparallel to represent a logic 1 or a low resistance when the vectors are parallel to represent a logic 0. The states stored in the element can be read by passing a sense current through the element and sensing the difference between the resistances.
The magnitude of the magnetic field used to switch the magnetic vector is proportional to the magnitude of the current through the conductor. To reduce power consumption, it is desirable to increase the field per current ratio of the conductor. One conventional technique of increasing the field per current ratio is to provide a magnetic liner for conductors. Magnetic liners for conductors are described in, for example, Naji et al., “A low power 1Mbit MRAM based on ITIMTJ bit cell integrated with Copper Interconnects, VLSI Conf. (2002)”, which is herein incorporated by reference for all purposes.
FIG. 1 shows a cross-sectional view of a conductor 160 with a magnetic liner 175. As shown, the cross-section of the conductor comprises a rectangular shape. The magnetic liner lines the sides and bottom surface of the conductor. However, it has been found that the sharp corners 178 at the sides and bottom of the conductor prevent the magnetic field from being concentrated in the liner. This results in the magnetic field being spread out in the corners, thus reducing the effectiveness of the liner. For example, such magnetic liners have been measured to improve the gain of the magnetic field for a given current by only about 2.
From the above discussion, there is desire to provide a magnetic liner for a conductor which can more effectively and efficiently concentrate the magnetic field therein.